Miniature inductive assembly



.. June 2, 1959 D. R. SCHMITIZ 2,

MINIATURE INDUCTIVE ASSEMBLY Filed Feb. 21, 1956 //v VE/V TOR D. R.SCHM/TZ fw mm A T TORNEV United States Patent Patented June 2, 19592,889,524 MINIATURE INDUCTIVEASSEMBLY llor'is R. Schmitz, Morristown,N.J., assignor to Bell Telephone Laboratories, Incorporated, New York,N.Y., a corporation of New.York

Application February 21, 1956, Serial No. 566,835

Claims. (Cl. 336-192) This invention relates to inductive devices andmore Particularly to miniaturized inductance devices, such ascommunication transformers.

In the design of communication transformers, for example, for use incarrier telephone systems, the comparatively recent development of highpermeability magnetic core materials, such as the polycrystallineceramic-like ferrites disclosed in the Patents 2,452,529, 2,452,530, and2,452,531, to I. L. Snoek, allows marked reduction in the size of themagnetic core. In order to obtain the advantages of decreased sizeafforded by the use of ferrites, it is desirable to employ windings offine wire. In low voltage applications, wire as fine as 46-gauge (0.0016inch diameter) is desirable.

In attempting to attain a high degree of miniaturization in the past, ithas been found that a limiting factor in the reliability of the deviceshas been the likelihood of'breakage of the fine wire, particularly ofthe leads in the region of attachment to their terminals. Another factorof importance in the design of miniaturized inductive devices is, thatwith decreased size, when employing conventional designs, a high degreeof skill and manual dexterity of the assembler is required. Primarycauses of winding failures have been found to be improper manipulationduring the assembly, in particular, the steps of securing the winding tothe terminal, and because of stress applied to the windings due torelative movement of the winding assembly with respect to the terminals.

It is desirable for moisture and mechanical protection to encapsulate orpot devices of this type in catalyzed, thermosetting or thermoplasticsealing compounds. The failure of a winding or lead due to any causeresults in a totally defective nonrepairable component owing to theextreme difliculty in removing the sealing compound. Therefore, thereliability of leads is of prime practical importance in the design ofminiature inductive devices.

Accordingly, it is a general object of this invention toattainminiaturized inductive devices having a high degree of reliability.

More specific objects of this invention are to provide a miniatureinductor or transformer of simple design and low cost in which theterminals constitute a pro tective enclosure for the winding assembly;to prevent relative movement of the winding assembly with respect to theterminals; and to enable the securing of all the fragile winding leadssimultaneously to their respective terminals with a minimum of strainthereon and requiring a minimum of skill and mechanical dexterity of theassembling operator.

These objects are accomplished in accordance with one specificembodiment of this invention comprising an insulating terminal plate orbutton having a plurality of wire segments extending therethrough andarranged in a spaced or circular array to form a cage-like structure onat least one side of the terminal plate. A winding bobbin having notchedflanges corresponding to the terminals is nested coaxially within thecage-like structure. One U-shaped magnetic core part is positionedbetween the terminal plate and one flange of the bobbin and extends intothe cage-like structure. Overlying the outer flange of the bobbin is asecond U-sha'ped magnetic core part the ends of which are cemented tothe ends of the first core part. Wound upon the bobbin between theflanges are a plurality of turns of insulated wire comprising thewinding or windings of the inductive device. The lead ends of thewindings pass through openings in the outer bobbin flange, are fannedoutward, and are secured to certain of the terminal wires. I

As discussed above, it is necessary in miniature devices of this type toinsure against relative motion of the winding, winding spool, terminals,and magnetic core. Particularly, it is important to prevent motionbetween the winding or windings and the terminals to which their endsare secured, which motion can introduce strains into the winding ends orrupture the electrical connection between the winding and the terminal.In accordance with one aspect of this invention, a tensioned insulatingband encircles the terminals between the bobbin flanges mechanicallybiasing them by distorting them slightly against the bobbin flanges andthereby maintaining the bobbin immobile with respect to the terminals.Motion between other parts of the device is prevented by seating thebase of the magnetic core in a depression in the insulating terminalplate through which the terminals extend and by proportioning the partsso that the lower notched flange of the winding spool rests on the uppersurface of the base of the core.

An appreciation of the size of miniature inductors in accordance withthis invention can be gained from the fact that the overall volume ofone specific illustrative embodiment comprising a carrier frequencytransformer is less than one-half cubic inch exclusive of externalterminals. The attainment of such a degree of miniaturization byutilizing ferrite core material and exceedingly fine wire windingsimposes severe requirements on the connections between the windings andthe terminals and on the making of such connections. Specifically, notonlymust relative motion between the parts that would tend to rupturethe very fine wire connections be pre vented, but also, in accordancewith another aspect of this invention, the structure must be such as tolend itself readily to fabrication without the introduction of strainsor deleterious forces during the fabrication by relatively unskilledpersonnel.

One feature of this invention relates to the arrangement of terminalsforming a protective cage for the winding assembly of the device.

Another feature involves the winding bobbin having discontinuitiescorresponding to the terminals whereby the bobbin and winding arepositioned coaxially within the terminal cage.

Another feature relates to the terminals extending beyond the bobbinflange to afford a point for simultaneous attachment by dip soldering ofall of the winding leads at a remote point on the terminal.

Another feature involves the employment of a tensioned band mechanicallyto bias the terminals in and about the winding bobbin to preventmovement of the bobbin parallel to the terminals.

Still another feature resides in the arrangement of the winding bobbinwhereby it serves to clamp the magnetic core securely in positionagainst the terminal plate.

These and other features of this invention may be understood byreference to the following detailed de scription and to the accompanyingdrawing, in which:

Fig. 1 is an exterior view of a completed assembly in accordance withthis invention;

Fig. 2 is an elevational view of the device of Fig. l with the enclosureshown in section for clarity; and

Fig. 3 is an exploded and enlarged representation of the device of Fig.1.

Referring now to Figs. 1 and 2, a transformer assembly may be seencomprising generally a terminal plate 11 of insulation such as moldedphenolic material in the form of a circular disk having a peripheralstep 12 in one face. Passing through the terminal plate at right anglesto its major faces are a plurality of wires 13 constituting theterminals of the transformer. Enclosing the assembly is a tubularhousing 14 having a rolledover lip 15 at one end corresponding to theperipheral step 12 in the terminal plate 11. Enclosing the open end ofthe tubular member is an insulating disk 17.

The terminal wires 13 are arranged in a circular array. Positionedwithin the cage-like structure formed by the terminal wires 13 on oneside of the terminal plate is a coil bobbin about which a plurality ofturns 21 of insulated wire are wound. The winding terminations or leads22 pass through openings or slots 41, seen in Fig. 3, in a flange 23 ofthe bobbin 20 and are wound about certain terminal wires 13 near theadjacent end of the wires 13.

Between the terminal plate 11 and the bobbin 20 is a U-shaped magneticcore part 25 of, for example, manganese zinc ferrite. The bottom surfaceof the core part 25 rests in a groove 28 in the terminal plate 11 andthe legs 26 and 27 of the core part are upturned, the leg 26 beingsubstantially on the common axis of the coil bobbin 20 and the terminalwires 13. The leg 27 extends upward outside of the cage of terminalwires 13. The core part leg 26 is positioned to extend through a lowerflange 24 and into a central opening 30 in the coil bobbin 20, best seenin Fig. 3. A core part 29 similarly of U configuration is positionedover the outer flange 23 of coil bobbin 20, with legs 31 and 32 of corepart 29 in juxtaposition with those of the core part 25. The core parts25 and 29 are cemented together and thereby define a closed rectangularmagnetic core structure having one side passing through the centralopening 30 in the coil bobbin 20 and an adjacent side clamped by thecoil bobbin 20 against the terminal plate 11.

Encompassing the terminals in the region intermediate the outer flange23 and an inner flange 24 of the bobbin 20 is a tensioned insulatingband 35, for example, a plurality of turns of insulating pressuresensitive tape. The band is tightly wound around the terminal wires 13and in so doing mechanically biases them into corresponding notches 36in the bobbin flanges as is best seen in Fig. 2. The terminal wiresections between the flanges 23 and 24 are bowed inward slightly by theband 35 thereby preventing movement of the coil bobbin 20 along theterminal wires 13. In Fig. 2, the bowing of the terminal wires 13 isexaggerated for the purposes of illustration. Several notches 36 in thebobbin flanges 23 and 24 prevent movement of the winding assemblyperpendicular to the axis of the terminal array while the band 35 ofinsulating tape and bowed portion of the terminals effectively preventmovement of the bobbin 20 in a direction generally parallel to theterminal wires 13 and away from the terminal plate 11. The core part 25,clamped between flange 24 of bobbin 2i) and terminal plate 11, preventsmovement of the bobbin 20 toward the terminal plate 11. In thisarrangement, the winding, although a separate assembly from the magneticcore and terminals, is positively fixed with respect to those elementsin the transformer. The leads of the winding need traverse only theshort distance from the bobbin 20 to the terminal wire ends within theprotective cage thereby minimizing the likelihood of breakage.

The details of the transformer of Figs. 1 and 2 may be more clearly seenby reference to Fig. 3 which is an exploded view of the winding and coreassembly. The tubular enclosure 14 is shown with the lip portion 15 atlead except for the molten solder.

the bottom in position to receive the terminal plate 11 with embeddedterminal wires 13. The groove 28 in which the core part 25 rests isclearly shown extending into the circular array of terminal wires 13.The terminal wires 13 may be unequally spaced in the array foridentification purposes and to fit a particular mounting for the device.Positioned to encompass the cage structure of terminal wires 13 istensioned band 35, only a fragment of which is shown in Fig. 3. The corepart 25, as well as the core part 29, includes legs 26 and 32,respectively, which are arranged to extend into the substantiallyrectangular hole 30 in the winding bobbin 20. Legs 27 and 31 fit alongflattened edges 40 of the flanges 23 and 24 of the bobbin 20. Thewinding leads 22 may be seen emerging from slots 41 in the flange 23 ofthe bobbin in a position convenient for attachment to the terminal ends..Uppermost in Fig. 3 is the insulating disk 17 which serves to completethe assembly after filling the enclosure 14 with a sealing compoundhaving good insulating qualities.

In assembly, the core part 25 is positioned in groove 28 and bobbin 20having turns 21 thereon is slid into the cage formed by terminals 13coming to rest on core part 25. Band 35 shown in Fig. 2 is placed aboutthe terminals 13 between'flanges 23 and 24 and is drawn up tight forcingthe terminal wires 13 into notches 36 of bobbin 20. The winding leadsare drawn through the slots 41 in the winding flange 23, are separated,stripped of insulation, if necessary, and wound about the correctterminal. The entire assembly then is inverted and the ends of theterminal wires 13 adjacent the bobbin 20 are immersed in 'a moltensolder bath to secure all of the winding leads to their terminalssimultaneously. After this step, the

core part 29 is positioned over bobbin 20 and cemented to the core part25. After a dip coating of insulation or after vacuum impregnation withwax, the transformer assembly is complete and in usable form. To prevent'closed in the tubular housing 14 which is subsequently filled with asealing compound and closed with disk 17; the sealing compound is alsoomitted from the drawing for clarity sake. In this form, the onlyexposed elements connected to the winding leads are the terminal endswhich are the extreme opposite ends from the point of lead attachment.Therefore, movement of a terminal wire has virtually no chance ofproducing strain in its winding lead. Similarly, the leads duringmanufacture are subjected only to handling in being threaded through thebobbin slots and wound about the terminal wire. Soldering isaccomplished with no physical contact to the These features, in additionto the arrangement for effectively securing the winding assembly as awhole from moving with respect to the terminal wires, practicallyeliminate the introduction of unwanted strain into the Winding leadsresulting in increased reliability in the transformer. I

It is to be understood that the above described arrangements are merelyillustrative of the application of the principles of this invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention.

What is claimed is:

1. An inductive assembly comprising an insulating terminal plate, aplurality of spaced terminals extending through said terminal plate andsecured therein, the portions on one side of said terminal plate forminga cagelike structure and the portions on the opposite side of saidterminal plate constituting the external connectors for the inductiveassembly, an insulating winding bobbin including end flanges and acentral opening extending through said bobbin positioned within saidcage-like structure with the end flanges extending transverse to theterminals, a. winding on said bobbin, a magnetic core for said windingpositioned at least partially within said cagelike structure and havinga portion extending through said winding bobbin, the ends of saidwinding emerging from said bobbin and secured each to a respectiveterminal, and insulating means encompassing said terminals between theend flanges and mechanically biasing said terminals against said windingbobbin end flanges tending to bow said terminals in the region betweenthe end flanges to secure said Winding bobbin from movement.

2. An inductive assembly comprising an insulating terminal plate, aplurality of spaced terminals extending through said terminal plate andsecured therein, the portions on one side of said terminal plate forminga generally circular cage-like structure and the portions on theopposite side of said terminal plate constituting the externalconnectors for the inductor assembly, an insulating winding bobbinincluding a central opening positioned within said cage-like structure,said bobbin including a pair of spaced end flanges in contact with saidterminals and being positioned thereby substantially coaxially withinsaid cage-like structure, a winding on said bobbin, a magnetic core forsaid winding including a portion extending through the opening in saidwinding bobbin, the ends of said winding emerging from said bobbin andsecured each to a respective terminal, and insulating means encompassingsaid terminals between the end fl-anges of said Winding bobbin andmechanically biasing said terminals against said winding bobbin tendingto bow said terminals in the region between the end flanges to securesaid winding bobbin from movement.

3. An inductive assembly comprising an insulating terminal plate, aplurality of spaced terminals extending through said terminal plate andsecured therein, the portions on one side of said terminal plate forminga generally circular cage-like structure and the portions on theopposite side of said terminal plate constituting the external terminalsfor the inductive assembly, an insulating winding bobbin having acentral opening therethrough positioned within said cage-like structure,said bobbin including a pair of spaced end flanges in contact with saidterminals and being positioned thereby substantially coaxial'ly Withinsaid cage-like structure, said flanges having peripheral notches thereincoinciding with the terminals, a winding on said bobbin, a magnetic corefor said winding including a portion extending through the opening insaid Winding bobbin, the ends of said winding emerging from said bobbinand secured each to a respective terminal, and insulating meansencompassing said terminals between the end flanges of said windingbobbin and me chanically biasing said terminals against said windingbobbin at the peripheral notches tending to bow said terminals in theregion between the end flanges to secure said winding bobbin frommovement.

4. The inductive assembly in accordance with claim 3 wherein saidinsulating means comprises a closed tensioned band.

5. The inductive assembly in accordance with claim 3 wherein saidinsulating means comprises a band of pressure sensitive tape.

6. An inductive assembly comprising an insulating terminal plate, aplurality of spaced terminals extending through said terminal plate andsecured therein, the portions on one side of said terminal plate forminga cagelike structure and the portions on the opposite side of saidterminal plate constituting the external connectors for the assembly, aninsulating winding bobbin having a central opening therethroughpositioned within said cage-like structure, said bobbin including endflanges having peripheral notches coinciding with the terminals, awinding on said bobbin, insulating means mechanically biasing saidterminals into the peripheral notches of said bobbin end flanges and amagnetic core extending through said bobbin and said winding, saidmagnetic core including a portion extending between said terminal plateand one bobbin end flange and secured therebetween.

7. An inductive device comprising a terminal plate of insulation, aplurality of elongated terminals secured in spaced array through saidplate with portions extending from opposite sides thereof, the terminalportions on one side of the plate defining a cage-like enclosure andthose on the other side being the external connectors, an insulatingwinding form within the enclosure including extended portions in contactwith said enclosure, a winding on the form, winding ends protruding fromthe form within the enclosure and secured to respective terminals onlyin a region of said terminals remote from said terminal plate, and atensioned band of insulation encompassing the terminals in the region ofsaid extended portions of said winding form to bias said terminalsagainst the winding form tending to bow said terminals in the regionbetween the extended portions of said winding form to inhibit relativemovement between the form and the terminals.

8. An inductive device comprising a plurality of terminal conductorsarranged in a cage-like array, an insulating winding spool including endflanges within said array, a winding on said spool having its endsconnected to respective ones of said conductors, and means forpreventing relative motion between said conductors and said windingspool, said means including a tensioned band of insulation encompassingsaid conductors mechanically to bias said conductors against the endflanges of said winding spool.

9. A miniature inductive device comprising an insulating terminal platehaving a depression in one side thereof, a plurality of terminalsextending through said plate and arranged in a cage-like array adjacentto said one side of said plate, an insulating winding spool within saidarray and having a central aperture and spaced flanges having peripheralnotches therein, a winding on said spool having its ends connected tosaid terminals, a magnetic core having one arm extending through saidaperture, said core having a portion positioned in said depression, anda tensioned band of insulation encompassing said terminals between theflanges of said winding spool and mechanically biasing said terminalswithin said notches in said flanges.

10. A miniature inductive device in accordance with claim 9 wherein oneof said flanges rests on a portion of said core and secures said core insaid depression.

References Cited in the file of this patent UNITED STATES PATENTS2,392,701 Sanders Jan. 8, 1946 2,535,203 Guthman Dec. 26, 1950 2,771,663Henry Nov. 27, 1956 2,774,051 McCarthy Dec. 11, 1956

